Have someone turn the wheel while you are under the truck, look near the steering gearbox area on the frame when its turning. Keep a close eye for any broken are cracked areas. With the truck being lifted there is a LOT of extra force on that section.
My 92 had the cross member break off right by the gearbox. $400 later it was all reinforced and welded together.
You also have death wobble in the title? That might clue more to the frame being damaged and the steering being effected. OR you need new linkages.
If the frame is actually flexing, engineer and fabricate a brace that will eliminate the flex. If it is flexing it will eventually crack. Many years ago I had a Dodge chassis under a motorhome that drove poorly due to frame flex in the area of the steering box. I fabricated an angle brace that eliminated the flex and the unit drove much better.
i have a 82 f250 with dana 60 axle.the truck also has 8in lift,3 in body. when i trun the wheel, back and forth, you can see the front fram flex a lot.is there any way to take some , of the flex out.
Just curious, what size tires are on this? Your going to have a lot more stress and flex with the truck parked vs in motion. Are you thinking the frame flex and death wobble are connected? Death wobble can be caused by the tires being out of balance more often than other issues. The bigger they are, the more this happens, although I've seen stock tires cause the wobble as well. If the tires are correctly balanced, check the front end componets, all of them for any play or wear. With "all" the lift on the truck have the drive line angles been corrected? Pitman arm, etc?